Channel state information transmission/reception method and apparatus of downlink coordinated multi-point communication system

ABSTRACT

A Channel State Information (CSI) transmission/reception method and an apparatus for transmitting/receiving CSI efficiently in a Coordinated Multi-Point (CoMP) communication system are provided. The CSI transmission method of a terminal for receiving Joint Transmission (JT) from a first Transmission Point (TP) and a second TP includes receiving a first CSI Reference Signal (CSI-RS) corresponding to the first TP, receiving a second CSI-RS corresponding to the second TP, generating an aggregated CSI corresponding to the first and second CSI-RSs, and transmitting the aggregated CSI, wherein generating an aggregated CSI comprising creating the aggregated CSI with a transmission timing of the aggregated CSI. The CSI transmission/reception method and apparatus is capable of transmission CSI efficiently in the CoMP system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of prior application Ser.No. 13/856,134, filed on Apr. 3, 2013, and claims the benefit under 35U.S.C. §119(e) of a U.S. provisional application filed on Apr. 6, 2012in the U.S. Patent and Trademark Office and assigned Ser. No.61/621,168, and under 35 U.S.C. §119(a) of a Korean patent applicationfiled on Apr. 2, 2013 in the Korean Intellectual Property Office andassigned Serial No. 10-2013-0035869, the entire disclosure of each ofwhich is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and an apparatus fortransmitting/receiving Channel State Information (CSI) in a CoordinatedMulti-Point (COMP) communication system.

2. Description of the Related Art

A communication system has uplink and downlink channels. The downlinkchannels are established for transmission from at least one TransmissionPoint (TP) to User Equipments (UEs). The uplink channels are establishedfor transmission from the UEs to at least one Reception Point (RP). TheUE is typically referred to as a terminal or a mobile station. The UEcan be a fixed UE or a mobile UE. The UE can be any one of a radiodevice, a cellular phone, a personal computer device, and the like. TheTP or RP is typically a fixed station. The TP and RP can be integratedinto a single device which can be referred to as base station. The basestation can be referred to as any one of a Base Transceiver System(BTS), a Node B, an enhanced Node B (eNB), an Access Point (AP), and thelike.

The communication system supports transmission of diverse signalsincluding a data signal, a control signal, and a reference signal. Thedata signal carries information content. The control signal is capableof processing the data signal appropriately. The reference signal canalso be referred to as a pilot signal. The reference signal is capableof coherent demodulation on the data and control signals. The referencesignal makes it possible to generate the Channel State Information (CSI)corresponding to the estimation value of the channel medium.

The Uplink (UL) data is carried by a Physical Uplink Shared Channel(PUSCH). The UE transmits a PUSCH, and the UL Control Information (UCI)is transmitted through Physical Uplink Control Information (PUCCH) withthe exception of the case where the UE is capable of transmitting thedata and a part of UCI through the PUSCH. The UCI includesacknowledgement (ACK) information in association with a Hybrid AutomaticRepeat Request (HARQ) process. The HARQ-ACK is of acknowledging thereceipt of the Transport Blocks (TB) transmitted to the UE in downlinkof the communication system and corresponds to the signal transmittedfrom the Node B to the UE.

The DL TBs are transmitted on a Physical Downlink Shared Channel(PDSCH). The UCI may include at least one of a Channel Quality Indicator(CQI), a Precoding Matrix Indicator (PMI), and a Rank Indicator (RI).The CQI, PMI, and RI can be integrally referred to as Channel StateInformation (CSI). The CQI provides the Node B with the Signal toInterference and Noise Ratio (SINR) which the UE experiences acrosssub-bands or entire DL operating bandwidth (BW). Typically, themeasurement value is provided in the form of the best Modulation andCoding Scheme (MCS) level at which a predefined BLock Error Rate (BLER)is accomplished. The Node B can be notified of the method of combiningthe signals transmitted from the UE to the Node B antennas in aMultiple-Input Multiple-Output (MIMO) scheme with PMI/RI. The UE iscapable of transmitting the UCI on PUCCH in separation from data orPUSCH along with data.

The DL data is transmitted on PDSCH. The DL Control Information (DCI)includes at least one of a DL CSI feedback request, a UL SchedulingAssignments for PUSCH transmission (UL SAs), and a DL SchedulingAssignments for PDSCH reception (DL SAs). The SAs are notified by theDCI formats transmitted on a Physical Downlink Control Channel (PDCCH).In addition to SAs, the PDCCHs may carry a common DCI for all UEs or agroup of UEs.

FIG. 1 is a graph illustrating a resource for use in a Long TermEvolution-Advanced (LTE-A) system according to the related art.

Referring to FIG. 1, in the LTE and LTE-A, the DL transmission isperformed in a unit of a time-domain subframe and a frequency-domainResource Block (RB). A subframe spans 1 msec, and an RB consists of 12subcarriers corresponding to the transmission bandwidth of 180 kHz. Asshown in FIG. 1, the system bandwidth of LTE-A is divided into pluralRBs in the frequency domain and plural subframes in the time domain.

The LTE-A Release 10 and beyond systems may operate with differentsignals. In downlink, the following reference signals are transmitted.

1. A Cell Specific Reference Signal (CRS): Used in an initial systemaccess, paging, a PDSCH demodulation, a channel measurement, a handover,and the like.

2. A Demodulation Reference Signal (DMRS): used for demodulation of aPDSCH.

3. A Channel Status Information Reference Signal (CSI-RS): Used forchannel measurement.

In addition to these reference signals, zero-power CSI-RS can be adoptedto the LTE-A release 10. Although the zero power CSI-RS may occur at thesame time and frequency resources as the normal CSI-RS, it differs fromthe normal CSI-RS in that the REs to which the zero power CSI-RS aremapped have no transmission. The zero power CSI-RS aims at muting CSI-RStransmission of a specific TP on the resource used by the adjacent TPsso as to avoid interference to the CSI-RSs transmitted by the adjacentTPs.

FIG. 2 is a diagram illustrating an RB for use in an LTE/LTE-A systemaccording to the related art.

Referring to FIG. 2, the RB consists of Resource Elements (REs) to whichdiverse reference signals, PDSCH, zero power CSI-RS and control channelsare mapped. It is noted that FIG. 2 shows a single RB in the frequencydomain and a single subframe in the time domain. A subframe may includea plurality of RBs that can be used for transmitting the aforementionedsignals. In FIG. 2, the resources marked with A, B, C, D, E, F, G, H, I,and J correspond to 4 CSI-RS ports. For example, the 4 REs marked with‘A’ are used for CSI-RS transmission with 4 antenna ports. The CSI-RS of2 antenna ports can be transmitted on the resource acquired byrestricting the resource for CSI-RS of 4 antenna ports to 2.Additionally, the CSI-RS of 8 antenna ports can be transmitted on theresource acquired by combining the two resources for CSI-RS of the 4antenna ports. The zero power CSI-RS can be mapped to the resources forCSI-RS of 4 antenna ports.

In the DL transmission mode 9 of the 3rd Generation Partnership Project(3GPP) LTE-A release 10, the UEs measures the CSI-RS transmitted by theeNB and feeds back downlink Channel Status Information (CSI), such asRI, PMI, and CQI. The RI, PMI, and CQI are reported at the respectivetimings indicated by the eNB. In a CSI feedback, PMI is calculated basedon the most recently reported RI while CQI is calculated under theassumption of the most recently reported RI and PMI.

Meanwhile, one of the key issues in the communication systems is theenhancement of a cell area and system throughput. The CoordinatedMulti-Point (CoMP) transmission/reception is one of the significanttechniques to accomplish these aims. The CoMP relies on the fact thatthe UE located at the cell edge is capable of receiving the downlinksignal transmitted via a set of TPs more reliability (DL CoMP) andtransmitting the uplink signal via a set of RPs more reliably (UL CoMP).The DL CoMP may include the relatively simple interference avoidancemethods, such as a coordinated scheduling and complex methods requiringaccurate and detailed channel information, such as a coordinatedtransmission of plural TPs. The UL CoMP may include the simple methods,such as a PUSCH scheduling in consideration of a single RP and morecomplex methods based on the received signal characteristics frommultiple RPs and in consideration of interference.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present invention.

SUMMARY OF THE INVENTION

Aspects of the present invention are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentinvention is to provide an improved Channel State Information (CSI)feedback method and an apparatus that is capable of transmitting CSIefficiently in the Coordinated Multi-Point (CoMP) system.

In accordance with an aspect of the present invention, a CSItransmission method of a terminal for receiving Joint Transmission (JT)from a first Transmission Point (TP) and a second TP is provided. Themethod includes receiving a first CSI Reference Signal (CSI-RS)corresponding to the first TP, receiving a second CSI-RS correspondingto the second TP, generating an aggregated CSI corresponding to thefirst and second CSI-RSs, and transmitting the aggregated CSI, whereinthe generating of the aggregated CSI comprises creating the aggregatedCSI with a transmission timing of the aggregated CSI.

In accordance with another aspect of the present invention, a terminalfor receiving JT from a first TP and a second TP is provided. Theterminal includes a transceiver which transmits a first CSI-RScorresponding to the first TP and a second CSI-RS corresponding to thesecond TP, and a controller which generates an aggregated CSIcorresponding to the first and second CSI-RSs, wherein the transceivertransmits the aggregated CSI, and the controller generates theaggregated CSI-RS with a transmission timing of the aggregated CSI.

In accordance with another aspect of the present invention, a CSIreception method of a higher layer device is provided. The methodincludes transmitting a first CSI-RS, receiving an aggregated CSIincluding an aggregated Channel Quality Indicator (CQI) from a terminal,acquiring a phase difference value based on reception timing of theaggregated CSI, and scheduling the terminal based on the aggregated CQIand the phase difference.

In accordance with another aspect of the present invention, a higherlayer device for receiving CSI is provided. The device includes atransceiver which transmits a first CSI-RS and receives an aggregatedCSI including an aggregated CQI from a terminal, and a controller whichacquires a phase difference value based on reception timing of theaggregated CSI and schedules the terminal based on the aggregated CQIand the phase difference.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a graph illustrating a resource for use in a Long TermEvolution-Advanced (LTE-A) system according to the related art;

FIG. 2 is a diagram illustrating a Resource Block (RB) for use in anLTE/LTE-A system according to the related art;

FIG. 3 is a diagram illustrating an architecture of a mobilecommunication system capable of a Coordinated Multi-Point (CoMP)communication according to an exemplary embodiment of the presentinvention;

FIG. 4 is a diagram illustrating a Channel Status Information ReferenceSignal (CSI-RS) resource allocation pattern for use in a CoMPcommunication according to an exemplary embodiment of the presentinvention;

FIG. 5 is a diagram illustrating CSI feedback timings for two CSI-RSresources in a Channel Quality Indicator (CQI) transmission methodaccording to a first exemplary embodiment of the present invention;

FIG. 6 is a block diagram illustrating a configuration of a UserEquipment (UE) according to an exemplary embodiment of the presentinvention;

FIG. 7 is a block diagram illustrating a configuration of an enhancedNode B (eNB) according to an exemplary embodiment of the presentinvention;

FIG. 8 is a flowchart illustrating a CSI feedback procedure of a UEaccording to an exemplary embodiment of the present invention; and

FIG. 9 is a flowchart illustrating a CSI reception procedure of an eNB(or a higher layer device) according to an exemplary embodiment of thepresent invention.

Throughout the drawings, it should be noted that like reference numbersare used to depict the same or similar elements, features, andstructures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of theinvention. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of theinvention. Accordingly, it should be apparent to those skilled in theart that the following description of exemplary embodiments of thepresent invention is provided for illustration purpose only and not forthe purpose of limiting the invention as defined by the appended claimsand their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

By the term “substantially” it is meant that the recited characteristic,parameter, or value need not be achieved exactly, but that deviations orvariations, including for example, tolerances, measurement error,measurement accuracy limitations and other factors known to those ofskill in the art, may occur in amounts that do not preclude the effectthe characteristic was intended to provide.

There is a need of introducing a new Channel State Information (CSI)feedback for diverse Coordinated Multi-Point (CoMP) schemes forfacilitating DownLink (DL) CoMP in the Long Term Evolution-Advanced(LTE-A) system. The CSI feedback method of the related art is performedin consideration of a single Transmission Point (TP) and a singleCSI-Reference Signal (CSI-RS) for channel measurement and CSI feedback.Accordingly, it is difficult to apply the CSI feedback scheme of therelated art to the CoMP system supporting multiple TPs transmission withmultiple CSI-RS without modification. There is therefore a need of a newCSI feedback scheme for supporting multiple TPs transmission (or CSIfeedback for corresponding CSI-RS configurations). The feedbackmechanisms for the CoMP schemes can be summarized as following:

1. The CSI reports for multiple TPs can be characterized by one offollowing 1-1 to 1-4.

-   -   1-1. The enhanced Node B (eNB) allocates multiple CSI-RS        resources to a User Equipment (UE) for CSI report.    -   1-2. Each CSI-RS resource is used for the UE to measure DL        channel from a specific TP.    -   1-2-1. According to an exemplary embodiment of the present        invention, a single CSI-RS corresponding to multiple TPs is not        ruled out.    -   1-3. A set of CSI-RS resources (or corresponding TPs) allocated        to the UE for CSI report is referred to as “CoMP measurement        set”.    -   1-4. The eNB is capable of designating the transmission mode and        timing per feedback corresponding to each CSI-RS.

2. An additional feedback for a Dynamic TP Selection and a DynamicBlanking (DS/DB) can be applied. In this case, the system can becharacterized by one of the following 2-1 and 2-2.

-   -   2-1. Some TPs (e.g., macro Node Bs) are capable of muting data        transmission (e.g., performing zero power transmission) to help        DL data reception of the UEs attached to other TPs.    -   2-2. If specific TPs turn on and off the data transmission        (e.g., zero power transmission), the UE is capable of performing        additional feedback reflecting interference situation.

3. An additional feedback for Joint Transmission (JT) can be applied.The JT can be characterized by at least one of the following 3-1 and3-2.

-   -   3-1. Multiple TPs are capable of transmitting data to a UE        simultaneously.    -   3-2. In order for multiple TPs to perform JT, it is imperative        for the UE to perform additional feedback reflecting the JT        situation.

FIG. 3 is a diagram illustrating an architecture of a mobilecommunication system capable of a CoMP communication according to anexemplary embodiment of the present invention. FIG. 3 is directed to anexemplary case of the cellular mobile communication system includingthree cells. In the following description, the term ‘cell’ denotes thedata transmission area served by a specific TP, and each TP can be aRemote Radio Head (RRH) using the same cell IDentifier (ID) as the macroeNB. In addition, the TPs can be macro and/or pico cells using differentcell IDs.

A central controller 330 transmits and receives that to and from UEs301, 302, 311, and 321 and processes the data received and to betransmitted. Here, in the case that the TPs are the RRHs using the samecell ID as the macro eNB, the macro eNB can be referred to as centralcontroller. In the case that the TPs are the macro and/or pico cellsusing different cell IDs, a device managing the cells integrally can bereferred to as central controller.

Referring to FIG. 3, the cellular mobile communication system includesat least one cell 300, 310, and 330 and UEs 301, 311, and 321 receivingdata from the closest cells, and the UE 302 received data from the cells300, 310, and 320 through a CoMP transmission. The UEs 301, 311, and 321receiving data from the closest cell estimates channels using the CSI-RSof their serving cells and feed back to the central controller 330.However, the UE 302 receiving the data from the three cells 300, 310,and 320 in CoMP transmission mode has to estimate all the channels formthe three cells 300, 310, and 320. For the channel estimation of the UE302, the central controller 330 allocates three CSI-RS resourcescorresponding to the cells 300, 310, and 320. How the central controller330 allocates CSI-RS resources to the UE 302 is described hereinafterwith reference to FIG. 4.

FIG. 4 is a diagram illustrating a CSI-RS resource allocation patternfor use in a CoMP communication according to an exemplary embodiment ofthe present invention.

Referring to FIG. 4, the central controller 330 maps three CSI-RSs tothe sources 401, 402, and 403 for the UE 302 in CoMP mode to estimatethe channels from the cells 300, 310, and 320 and the channel forreceiving control information and system information and transmits theCSI-RSs on the corresponding resources. For example, the CSI-RS forchannel estimation of the cell 300 is mapped to the resource position401, the CSI-RS for channel estimation of the cell 310 to the resourceposition 402, and the CSI-RS for channel estimation of the cell 320 tothe resource position 403. As described above, a set of resourceincluding at least one resource allocated to the UE in CoMP mode forCSI-RS transmission or a set of the cells corresponding to the CSI-RSresources is referred to as CoMP measurement set.

In order to support a DS/DB technique, the central controller 330 iscapable of allocating to the UE 302 additional resource for use ininterference measurement. The data amount the UE 302 can receive perunit time is determined depending on the interference amount as well asthe signal strength. Accordingly, the central controller 330 mayallocate the Interference Measurement Resource (IMR) for the UE tomeasure the interference accurately. The eNB is capable of allocating tothe UE 302 a common IMR in order for the UE 302 to measure theinterference amount to the signal components for all CSI-RSs in themeasurement set or several IMRs in order for the UE to measure theinterferences for the zero power transmission situation and normaltransmission situation. Referring to FIG. 4, the UE 302 measures thesignals from the three cells 301, 311, and 321 using the three CSI-RSresources 401, 402, and 403. The UE 302 is capable of measuring theinterference occurring when it receives the signals from the three cellsusing the IMR resource 410. At this time, the eNB or the centralcontroller 330 is capable of controlling the signal transmission of theneighbor cells at the resource position 410 in order to reflect theinterference to the UE 302 accurately. The CSI report for CoMP can betransmitted on a Physical Uplink Control Information (PUCCH) inseparation of the data or on a Physical Uplink Shared Channel (PUSCH)along with data. Accordingly, it is imperative that the CSI report isperformed for CoMP on PUSCH and PUCCH, respectively.

As described above, the default feedback mode for multiple CSI-RS may bePer-CSI-RS-resource feedback for reporting individual channel states forthe respective CSI-RS resources. The UEs perform measurements on therespective CSI-RS resources for plural TPS to generate and feed backCSI. In the case of per-CSI-RS-resource feedback, the CSI is transmittedindividually for some or all of the CSI-RS resources. For example,assuming the CoMP measurement set of {CSI-RS-1, CSI-RS-2}, the centralcontroller sends the UE the Radio Resource Control (RRC) information toinstruct to generate the CSI-RS feedbacks for the two individualfeedback configurations. An example is provided below.

Exemplary Embodiment 1

1. UE's first feedback configuration: (Mode 1-1, N_(pd)=10,N_(OFFSET,CQI)=0, M_(RI)=2, N_(OFFSET,RI)=—1, CSI-RS-1).

2. UE′ second feedback configuration: (Mode 1-1, N_(pd)=10,N_(OFFSET,CQI)=2, M_(RI)=2, N_(OFFSET,RI)=—1, CSI-RS-2).

In Exemplary Embodiment 1, mode 1-1 means that the corresponding CSIfeedback includes a Rank Indicator (RI) and a wideband CQI/PrecodingMatrix Indicator (PMI). The wideband CQI/PMI report timing is thesubframes fulfilling(10×n_(f)+floor(n_(s)/2)−N_(OFFSET,CGI))modN_(pd)=0. Here, n_(f) denotesthe system frame number, and n_(s)={0, 1, . . . , 19} denotes the slotindices in the frame. N_(OFFSET,CQI) denotes the wideband CQI/PMI reportoffset (in a unit of a subframe), and N_(pd) denotes the widebandCQI/PMI period (in a unit of a subframe). The RI report interval is aninteger multiple (multiple of MO of the wideband CQI/PMI period N_(pd)(in a unit of a subframe). Moreover, floor(x) denotes the function forreturning maximum integer equal to less than x. For example, the RIreport instances are the subframes fulfilling(10×n_(f)+floor(n_(s)/2)−N_(OFFSET,CQI))mod(N_(pd)×M_(RI))=0. The RIreport offset N_(OFFSET,RI) is taken from the set {0, −1, . . . ,|(N_(P)−1)}. In the case that the RI and the wideband CQI/PMI collide,the wideband CQI/PMI drops.

FIG. 5 is a diagram illustrating CSI feedback timings for two CSI-RSresources in a CQI transmission method according to the first exemplaryembodiment of the present invention. The feedbacks for two differentCSI-RSs are performed at the respective timings independently.

Referring to FIG. 5, in consideration of JT, an additional CSI forcommon transmission from the TPs can be used in addition to thePer-CSI-RS-resource feedback. For example, in the case that the CSI-RSresources allocated to the UE include the CSI-RS resources for pluralTPs, the UE is capable of performing additional report of the CSI forthe set of CSI-RS resources, such as aggregated CQI for the situationwhere the phase differences among the TPs and/or JT are applied.

Suppose that the CoMP measurement set of the UE corresponding to TP-1and TP-2 having N₁ and N₂ antenna ports, respectively, is {CSI-RS-1,CSI-RS-2}and the individual CSIs determined for the two CSI-RSs arecharacterized by following sections 1 to 3:

1. CQI determined for TP-1 is CQI-1 and CQI determined for TP-2 isCQI-2.

2. Rank is determined as r for both TP-1 and TP-2.

3. Precoding matrices for TP-1 and TP-2 are P₁ and P₂.

Here, P₁ and P₂ have the size of N₁×r and N₂×r, respectively, and therespective PMIs are determined as the values corresponding to P₁ and P₂.If the additional feedback for JT is considered, the UE has to generateand report the aggregated CQI indicating the channel state in the JTsituation where the TP-1 and TP-2 transmit data simultaneously. Forexample, the aggregated CQI for the JP situation of TP-1 and TP-2 can begenerated under the assumption that the rank in the JT situation isequal to the common rank value r determined for the individual TP andthe precoding matrix with a size of (N₁+N₂)×r for JT situation is givenas

${P_{JT}(\theta)} = {\begin{bmatrix}P_{1} \\{\theta \cdot P_{2}}\end{bmatrix}.}$

Here, θ denotes one of the elements of the unit complex conjugate set

$\{ {^{j\; 2\pi \frac{0}{M}},^{j\; 2\pi \frac{1}{M}},^{j\; 2\pi \frac{2}{M}},\ldots,^{j\; 2\pi \frac{M - 1}{M}}} \}$

having size M. θ reflects the phase difference between two TPsparticipated in JT. Here, it can be a problem to determine which TP isreferenced for calculating the phase θ. For example, the eNB is capableof notifying the UE of the information indicating the reference pointfor calculating the phase θ. The eNB is capable of notifying the UE of afeedback index for specific CSI-RS corresponding to the reference pointor the index of CSI-RS (or TP). In this case, an RRC signaling or aPhysical Downlink Control Channel (PDCCH) can be used. In a modifiedexample, the eNB is capable of taking into consideration of the phasedifferences of other TPs based on the feedback or CSI-RS (or TP) withthe least index. In the above example, θ configured based on the TP-1 asreference point is the value indicating the phase difference of TP-2 toTP-1. In this case, the UE generates the aggregated CQI under theassumption of the phase difference of 0 and precoding matrix of

${P_{JT}(\theta)} = {\begin{bmatrix}P_{1} \\{\theta \cdot P_{2}}\end{bmatrix}.}$

Here, a method for determining θ as the value reflecting the phasedifference between TPs is considered in the situation where the UEgenerates a specific aggregated CQI and performs CQI feedback. In thisexemplary embodiment, the UE determines the 0 value for calculating theaggregated CQI in consideration of at least one of the two followingfactors:

1. aggregated CQI feedback time (timing),

2. frequency region corresponding to aggregated CQI feedback.

Table 1 shows an exemplary phase difference θ between TPs determinedaccording to the feedback timing of the wideband aggregated CQI as CSIinformation for downlink frequency wideband used by the UE.

TABLE 1 Feedback 1^(st) 2^(nd) 3^(rd) M^(th) (M + 1)^(th) timing reportreport report . . . report report . . . Phase difference θ between TPs$e^{j\; 2\pi \frac{s_{1}}{M}}$$e^{j\; 2\pi \frac{s_{1} + 1}{M}}$$e^{j\; 2\pi \frac{s_{1} + 2}{M}}$ . . .$e^{j\; 2\pi \frac{s_{1} + M - 1}{M}}$$e^{j\; 2\pi \frac{s_{1}}{M}}$ . . .

In the exemplary method for determining 0 based on Table 1, whenreporting i^(th) wideband aggregated CQI, the UE generates the widebandaggregated CQI under the assumption that 0 is the (s₁+i mod M)^(th)element of the set

$\{ {^{j\; 2\pi \frac{0}{M}},^{j\; 2\pi \frac{1}{M}},^{j\; 2\pi \frac{2}{M}},\ldots,^{j\; 2\pi \frac{M - 1}{M}}} \}$

of M values. In this exemplary embodiment, θ is determined in a periodicmethod predefined according to the report timing. Here, the start valueSi of θ can be 0, 1, or other fixed value or configured by the eNB tothe UE through RRC signaling. In addition, M can be a fixed value knownto the UE/eNB or a value notified from the eNB to the UE through RRCsignaling or other method.

In the above exemplary embodiment, the first report is not limited tothe initial report after the UE's attachment to the eNB but can be acertain time point determined randomly. Similarly, a randomly determinedtime point can be the first report timing in other exemplary embodimentsof the present invention.

In the exemplary method for determining θ according to another modifiedexemplary embodiment, the UE generates the wideband aggregated CQI underthe assumption that θ is the f(s₁+i)^(th) element of the set

$\{ {^{j\; 2\pi \frac{0}{M}},^{j\; 2\pi \frac{1}{M}},^{j\; 2\pi \frac{2}{M}},\ldots,^{j\; 2\pi \frac{M - 1}{M}}} \}$

of M values available for θ. Here, f(x) is a pseudo-random sequence orcorresponding function value outputting an integer value greater than 0and less than M−1. f(x) also can be another type of function outputtingan integer greater than 0 and less than M−1. The exemplary embodimentbased on Table 1 is directed to an example in the case of f(x)=(s₁+x modM). The eNB and the UE share the same information needed for calculatingf(x). For example, in the corresponding exemplary method, the startvalue Si can be 0, 1, or other fixed value or configured by the eNB tothe UE through an RRC signaling. In addition, M can be a fixed valueknown to the UE/eNB or a value notified from the eNB to the UE throughRRC signaling or other method.

Table 2 shows an example of the method for determining the phasedifference θ between TPs according to the sub-band index and feedbacktiming of the sub-band aggregated CQI in a situation where the downlinkfrequency band for the UE is divided into sub-bands of which CSIinformation are reported respectively.

TABLE 2 1^(st) 2^(nd) 3^(rd) M^(th) (M + 1)^(th) report report report .. . report report . . . Subband 1 $e^{j\; 2\pi \frac{s_{1}}{M}}$$e^{j\; 2\pi \frac{s_{1} + 1}{M}}$$e^{j\; 2\pi \frac{s_{1} + 2}{M}}$ . . .$e^{j\; 2\pi \frac{s_{1} + M - 1}{M}}$$e^{j\; 2\pi \frac{s_{1}}{M}}$ . . . Subband 2$e^{j\; 2\pi \frac{s_{2}}{M}}$$e^{j\; 2\pi \frac{s_{2} + 1}{M}}$$e^{j\; 2\pi \frac{s_{2} + 2}{M}}$ . . .$e^{j\; 2\pi \frac{s_{2} + M - 1}{M}}$$e^{j\; 2\pi \frac{s_{2}}{M}}$ . . . Subband 3$e^{j\; 2\pi \frac{s_{3}}{M}}$$e^{j\; 2\pi \frac{s_{3} + 1}{M}}$$e^{j\; 2\pi \frac{s_{3} + 2}{M}}$ . . .$e^{j\; 2\pi \frac{s_{3} + M - 1}{M}}$$e^{j\; 2\pi \frac{s_{3}}{M}}$ . . .

Subband L $e^{j\; 2\pi \frac{s_{L}}{M}}$$e^{j\; 2\pi \frac{s_{L} + 1}{M}}$$e^{j\; 2\pi \frac{s_{L} + 2}{M}}$ . . .$e^{j\; 2\pi \frac{s_{L} + M - 1}{M}}$$e^{j\; 2\pi \frac{s_{L}}{M}}$ . . .

In the exemplary method based on Table 2, when reporting the i^(th)aggregated CQI for the I^(h) sub-band, the UE generates the widebandaggregated CQI under the assumption that θ is the (s₁+i mod M)^(th)element of the set

$\{ {^{j\; 2\pi \frac{0}{M}},^{j\; 2\pi \frac{1}{M}},^{j\; 2\pi \frac{2}{M}},\ldots,^{j\; 2\pi \frac{M - 1}{M}}} \}$

of M values available for θ. In this exemplary embodiment, the value θis determined in a periodic method predefined according to the reporttiming and sub-band index. Here, the start values s₁, s₂, . . . , s_(L)(i.e., first row of Table 2) of θ for the respective sub-bands can be 0,1, or other fixed value or configured by the eNB to the UE through anRRC signaling. In a modified exemplary embodiment, the start values s₁,s₂, . . . , s_(L) can be set to different values as following methods:

Exemplary Method 1: s₁=(l−1), l=1, 2, . . . , L,

Exemplary Method 2:

${s_{l} = {\lfloor \frac{M}{L} \rfloor \cdot ( {l - 1} )}},{l = 1},2,\ldots,{L.}$

According to a modified exemplary embodiment, the eNB is capable ofnotifying the UE of the start values s₁, s₂, . . . , s_(L) through anRRC signaling or other communication method.

According to another modified exemplary embodiment, when reportingaggregated CQI for l^(th) sub-band, the UE generates the sub-bandaggregated CQI under the assumption that θ is the f(s₁+i)^(th) elementof the set

$\{ {^{j\; 2\pi \frac{0}{M}},^{j\; 2\pi \frac{1}{M}},^{j\; 2\pi \frac{2}{M}},\ldots,^{j\; 2\pi \frac{M - 1}{M}}} \}$

of M values. Here, f(x) is a pseudo-random sequence or correspondingfunction value outputting a value greater than 0 and less than M−1. f(x)also can be another type of function outputting an integer greater than0 and less than M−1. The exemplary embodiment based on Table 2 isdirected to an example in the case off(x)=(s₁+x mod M). The eNB and theUE share the same information needed for calculating f(x). In this case,the start values s₁, s₂, . . . , s_(L) can be 0, 1, or other fixed valueor configured by the eNB to the UE through RRC signaling. In addition, Mcan be a fixed value known to the UE/eNB or a value notified from theeNB to the UE through an RRC signaling or other method. L denotes anumber of sub-band indices. According to another modified exemplaryembodiment, the start values s₁, s₂, . . . , s_(L) can be set accordingto the following exemplary method 1 or exemplary method 2:

Exemplary Method 1: s₁=(l−1), l=1, 2, . . . , L,

Exemplary Method 2:

${s_{l} = {\lfloor \frac{M}{L} \rfloor \cdot ( {l - 1} )}},{l = 1},2,\ldots,{L.}$

According to a modified exemplary embodiment, the eNB is capable ofnotifying the UE of all the start values through an RRC signal or othercommunication method.

The above exemplary embodiment is proposed under the assumption thatwhen the rank values of both the two TPs are r identically the precodingmatrix for use in JT is determined as

${P_{JT}(\theta)} = {\begin{bmatrix}P_{1} \\{\theta \cdot P_{2}}\end{bmatrix}.}$

However, exemplary embodiments of the present invention are not limitedthereto. For example, an exemplary method for determining θ as the valuereflecting the phase difference between TPs can be considered even inthe situation where rank values for the two different TPs, i.e., TP-1and TP-2, are determined as different values of r₁ and r₂.

Suppose that the CoMP measurement set of the UE corresponding to TP-1and TP-2 having N₁ and N₂ antenna ports respectively is {CSI-RS-1,CSI-RS-2} and the individual CSIs determined for the two CSI-RSs arecharacterized by following sections 1 to 3 in consideration of thesituation where the rank values of the TPs are determined as differentvalues of r₁ and r₂:

1. CQI determined for TP-1 is CQI-1 and CQI determined for TP-2 isCQI-2.

2. Rank is determined as r₁ for TP-1 and r₂ for TP-2.

3. Precoding matrices for TP-1 and TP-2 are P₁ and P₂.

Here, P₁ and P₂ have the size of N₁×r and N₂×r respectively, and therespective PMIs are determined as the values corresponding to P₁ and P₂.If the aggregated CQI is considered as the additional feedback for JT,the aggregated CQI for the JT situation of TP-1 and TP-2 can begenerated under the assumption that the maximum value among individualTPs r_(JT)=max(r₁,r₂) is the rank under the JT situation and theprecoding matrix having the size of (N₁+N₂)×r_(JT) in JT situation isdetermined according to the exemplary method indicated by sections 1 and2 described below.

1. If r₁>r₂, the precoding matrix is assumed as

${P_{JT}(\theta)} = {{\begin{bmatrix}P_{1} \\{\theta \cdot \lbrack {P_{2},B_{N_{2} \times {({r_{JT} - r_{2}})}}} \rbrack}\end{bmatrix}\mspace{14mu} {or}\mspace{14mu} {P_{JT}(\theta)}} = {\begin{bmatrix}P_{1} \\{\theta \cdot \lbrack {B_{N_{2} \times {({r_{JT} - r_{2}})}},P_{2}} \rbrack}\end{bmatrix}.}}$

2. If r₁<r₂, the precoding matrix is assumed as

${P_{JT}(\theta)} = {{\begin{bmatrix}\lbrack {P_{1},B_{N_{1} \times {({r_{JT} - r_{1}})}}} \rbrack \\{\theta \cdot P_{2}}\end{bmatrix}\mspace{14mu} {or}\mspace{14mu} {P_{JT}(\theta)}} = {\begin{bmatrix}\lbrack {B_{N_{1} \times {({r_{JT} - r_{1}})}},P_{1}} \rbrack \\{\theta \cdot P_{2}}\end{bmatrix}.}}$

Here, B_(N×r) is one of the following matrices:

1. N×r zero matrix.

2. Specific N×r precoding matrix defined in LTE standard.

Under the assumption of precoding matrix for JT, θ denotes the phasedifference between TPs determined by feedback timing and/or sub-bandindex values according to the methods of above exemplary embodiments.

According to another exemplary embodiment, in the situation where therank values of the TPs are determined as different value of r₁ and r₂,the aggregated CQI for the JT situation of TP-1 and TP-2 can begenerated under the assumption that the rank in the JT situation is theminimum value among the ranks of the TPs r_(JT)=max(r₁,r₂) and theprecoding matrix having the size of (N₁+N₂)×r_(JT) in the JT situationis determined by the following methods:

1. If r₁>r₂, the precoding matrix is assumed as

${P_{JT}(\theta)} = {\begin{bmatrix}\lbrack P_{1} \rbrack_{N_{1} \times r_{2}} \\{\theta \cdot P_{2}}\end{bmatrix}.}$

2. If r₁<r₂, the precoding matrix is assumed as

${P_{JT}(\theta)} = {\begin{bmatrix}P_{1} \\{\theta \cdot \lbrack P_{2} \rbrack_{N_{2} \times r_{1}}}\end{bmatrix}.}$

Here, [P]_(N×r) is an N×r matrix determined by selecting r columns amongM columns of the matrix P having the size of N×M for M greater than r.Here, r columns are selected by a specific method shared between the eNBand the UE. Under the assumption of the precoding matrix for JT, θdenotes the phase different between TPs determined according to thefeedback timing and/or sub-band index values through the methods of theabove exemplary embodiments.

FIG. 6 is a block diagram illustrating a configuration of a UE accordingto an exemplary embodiment of the present invention.

Referring to FIG. 6, the UE includes a transceiver 1010, a channelestimator 1020, a feedback generator 1030, and a controller 1040. Thetransceiver 1010 transmits and receives control signals, data, andreference signals to and from the eNB. More particularly, in anexemplary embodiment of the present invention, the transceiver 1010 iscapable of receiving CSI-RS and transmitting CSI feedback including theaggregated CQI for JT of the TPs. The channel estimator 1020 measuresthe CSI-RS ports allocated for the UE. The feedback generator 1030generates individual CSI feedbacks for the plural TPs based on themeasurement values of the channel estimator 1020 and the CSI feedbacksincluding the aggregated CQI in consideration of the phase differencesamong the TPS for JT. All the above operations are controlled by thecontroller 1040. The controller 1040 controls the internal components ofthe UE to transmit the aggregated CQI according to one of the abovedescribed exemplary embodiments of the present invention.

FIG. 7 is a block diagram illustrating a configuration of an eNBaccording to an exemplary embodiment of the present invention.

Referring to FIG. 7, the eNB includes a controller 1110, a transceiver1120, and a resource allocator 1130. The transceiver 1120 transmits andreceives the control information, data, and reference signals with a UE.The transceiver 1120 transmits CSI-RS and receives CSI-RS feedbackincluding the aggregated CQI acquired in consideration of the phasedifferences among the TP for JT. The resource allocator 1130 allocatesCSI-RS resources and data resource to the UEs based on the CSI feedbacksfrom the UEs. All the above operations are controlled by the controller1110. The controller 1110 controls the internal components of the eNB totransmit the CSI-RS and receive the aggregated CQI according to one ofthe above-described exemplary embodiments of the present invention.

FIG. 8 is a flowchart illustrating a CSI feedback procedure of a UEaccording to an exemplary embodiment of the present invention.

Referring to FIG. 8, the feedback generator 1030 determines the rankvalues of the plural TPs participated in the JT and determines the rankvalue for use in the JP at step 1210. The rank value is determined asdescribed in the above exemplary embodiments. If it is configured togenerate the rank values of all TPs as the same value, step 1210 may beomitted.

The feedback generator 1030 determines the phase differences among theTPs according to the method for calculating the phase differences basedon the feedback timings of Table 1 or 2 and/or sub-band indices at step1220. In accordance with the corresponding phase differences, theprecoding matrix is determined. At step 1230, the feedback generator1030 acquires the aggregated CQI under the assumption of using theprecoding matrix which has been determined at step 1220.

The feedback generator 1030 generates a CSI including at least one ofthe acquired RI, PMI, and CQI and transmits the CSI by means of thetransceiver 1010 at step 1240. According to an exemplary embodiment ofthe present invention, the RI and PMI for JT are partially excluded forgenerating the CSI. The CSI including the aggregated CQI is referred toas aggregated CSI. According to a modified exemplary embodiment, theaggregated CSI is capable of including the information on the aggregatedPMI and/or aggregated RI acquired according to one of the abovedescribed exemplary embodiments.

FIG. 9 is a flowchart illustrating a CSI reception procedure of an eNB(or higher layer device) according to an exemplary embodiment of thepresent invention.

Referring to FIG. 9, the transceiver 1120 of the eNB transmits CSI-RS tothe UE at step 910. As described above, the CSI-RS resource position maybe predefined by the resource allocator 1130.

The transceiver 1120 receives the CSI including the aggregated CQI fromthe UE at step 920. As described above, the aggregated CQI resourceposition may be predefined by the resource allocator 1130.

The controller 1110 extracts the phase value corresponding to theaggregated CQI at step 930. The controller 1110 extracts the phase valueor phase value indicator corresponding to the aggregated CQI based onthe CSI transmission timings and/or sub-band indices according to one ofthe above described exemplary embodiments.

The controller 1110 performs scheduling based on the aggregated CQI andthe corresponding phase value at step 940. For example, the controller1110 is capable of selecting the phase value (i.e., an optimal phasevalue) corresponding to the best CQI among the plural aggregated CQIsreceived currently and previously and scheduling the UE based on theselected phase value. The controller 1110 is also capable of determiningthe phase value to be applied to the corresponding UE in considerationof the phase value corresponding to the best CQI and scheduling thecorresponding UE according to the determined phase value.

According to a modified exemplary embodiment, only the phase valueselection can be performed by a higher layer device, e.g., a centralcontroller, of the eNB. In this case, the eNB sends the aggregated CQIand the corresponding phase value (which may be replaced by informationneeded for calculating the other phase values) to the central controller330 such that the central controller 330 selects the phase value basedthereon and notifies the eNB of the selected phase value.

As described above, the CSI transmission/reception method and apparatusare capable of transmission CSI efficiently in the CoMP system.

It will be understood that each block of the flowchart illustrationsand/or block diagrams, and combinations of blocks in the flowchartillustrations and/or block diagrams, can be implemented by computerprogram instructions. These computer program instructions may beprovided to a processor of a general purpose computer, a special purposecomputer, or other programmable data processing apparatus to produce amachine, such that the instructions, which execute via the processor ofthe computer or other programmable data processing apparatus, createmeans for implementing the functions/acts specified in the flowchartand/or block diagrams. These computer program instructions may also bestored in a computer-readable memory that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablememory produce an article of manufacture including instruction meanswhich implement the function/act specified in the flowchart and/or blockdiagram block or blocks. The computer program instructions may also beloaded onto a computer or other programmable data processing apparatusto cause a series of operational steps to be performed on the computeror other programmable apparatus to produce a computer implementedprocess such that the instructions which execute on the computer orother programmable apparatus provide steps for implementing thefunctions/acts specified in the flowchart and/or block diagrams.

Furthermore, the respective block diagrams may illustrate parts ofmodules, segments or codes including at least one or more executableinstructions for performing specific logic function(s). Moreover, itshould be noted that the functions of the blocks may be performed indifferent order in several modifications. For example, two successiveblocks may be performed substantially at the same time, or may beperformed in a reverse order according to their functions.

The term “module” according to the exemplary embodiments of the presentinvention, means, but is not limited to, a software or hardwarecomponent, such as a Field Programmable Gate Array (FPGA) or anApplication Specific Integrated Circuit (ASIC), which performs certaintasks. A module may advantageously be configured to reside on theaddressable storage medium and configured to be executed on one or moreprocessors. Thus, a module may include, by way of example, components,such as software components, object-oriented software components, classcomponents and task components, processes, functions, attributes,procedures, subroutines, segments of a program code, drivers, firmware,microcode, circuitry, data, databases, data structures, tables, arrays,and variables. The functionality provided for in the components andmodules may be combined into fewer components and modules or furtherseparated into additional components and modules. In addition, thecomponents and modules may be implemented such that they execute one ormore CPUs in a device or a secure multimedia card.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method of a terminal in a communication system,the method comprising: receiving first configuration information andsecond configuration information; receiving a first channel stateinformation-reference signal (CSI-RS) associated with the firstconfiguration information; receiving a second CSI-RS associated with thesecond configuration information; generating channel state information(CSI) based on the first CSI-RS and second CSI-RS; and transmitting thegenerated CSI.
 2. The method of claim 1, wherein the first CSI-RScorresponds to a first transmission point (TP), and wherein the secondCSI-RS corresponds to a second TP.
 3. The method of claim 1, whereingenerating the CSI comprises generating the CSI with a transmissiontiming of the CSI.
 4. The method of claim 2, wherein generating the CSIcomprises generating the CSI using a transmission timing of the CSI anda sub-band indicator used by the terminal.
 5. The method of claim 4,wherein generating the CSI using the transmission timing of the CSIcomprises: acquiring a phase difference between the first and second TPsusing the transmission timing of the CSI; generating an channel qualityindicator (CQI) using the acquired phase difference and the first andsecond CSI-RSs; and generating the CSI including the CQI.
 6. The methodof claim 4, wherein generating the CSI using a transmission timing ofthe CSI comprises generating a precoding matrix indicator (PMI) usingthe acquired phase difference and the first and second CSI-RSs, andwherein generating the CSI including the CQI comprises generating theCSI including the CQI and the PMI.
 7. A method of a first transmissionpoint in a communication system, the method comprising: transmittingfirst configuration information; transmitting a first channel stateinformation reference signal (CSI-RS) associated with the firstconfiguration information; and receiving CSI based on the first CSI-RSand a second CSI-RS.
 8. The method of claim 7, wherein the first CSI-RScorresponds to the first transmission point (TP), and wherein the secondCSI-RS corresponds to a second TP.
 9. The method of claim 7, furthercomprising: acquiring a phase difference value based on reception timingof the CSI; and scheduling the terminal based on a channel qualityindicator (CQI) and the phase difference, wherein a CQI is included inthe received CSI.
 10. The method of claim 9, wherein the scheduling ofthe terminal based on the CQI and the phase difference comprisesselecting the phase difference value corresponding to a predeterminedCQI for scheduling.
 11. A terminal in a communication system, theterminal comprising: a transceiver configured to transmit and receive asignal; and a controller configured to: receive first configurationinformation and second configuration information, receive a firstchannel state information-reference signal (CSI-RS) associated with thefirst configuration information, receive a second CSI-RS associated withthe second configuration information, generate channel state information(CSI) based on the first CSI-RS and second CSI-RS, and transmit thegenerated CSI.
 12. The terminal of claim 11, wherein the first CSI-RScorresponds to a first transmission point (TP), and wherein the secondCSI-RS corresponds to a second TP.
 13. The terminal of claim 11, whereinthe controller is further configured to generate the CSI with atransmission timing of the CSI.
 14. The terminal of claim 12, whereinthe controller is further configured to generate the CSI using atransmission timing of the CSI and a sub-band indicator used by theterminal.
 15. The terminal of claim 14, wherein the controller isfurther configured to: acquire a phase difference between the first andsecond TPs using the transmission timing of the CSI, generate an channelquality indicator (CQI) using the acquired phase difference and thefirst and second CSI-RSs, and generate the CSI including the CQI. 16.The terminal of claim 14, wherein the controller is further configuredto: generate a precoding matrix indicator (PMI) using the acquired phasedifference and the first and second CSI-RSs, and generate the CSIincluding the CQI and the PMI.
 17. A first transmission point in acommunication system, the first transmission point comprising: atransceiver configured to transmit and receive a signal; and acontroller configured to: transmit first configuration information,transmit a first channel state information reference signal (CSI-RS)associated with the first configuration information, and receive CSIbased on the first CSI-RS and a second CSI-RS.
 18. The firsttransmission point of claim 17, wherein the first CSI-RS corresponds tothe first transmission point (TP), and wherein the second CSI-RScorresponds to a second TP.
 19. The first transmission point of claim17, wherein the controller is further configured to: acquire a phasedifference value based on reception timing of the CSI, and schedule theterminal based on a channel quality indicator (CQI) and the phasedifference, wherein a CQI is included in the received CSI.
 20. The firsttransmission point of claim 19, wherein the controller is furtherconfigured to select the phase difference value corresponding to apredetermined CQI for scheduling.